Autism spectrum disorder (ASD) constitutes a major public health concern, with an annual cost projected to reach nearly $500 billion within the next seven years. Attenuation of core challenges associated with ASD is possible with very early identification and intervention in infancy. Yet an acute lack of knowledge about the course of ASD in the early infant period remains a massive barrier to addressing this public health challenge and improving quality of life for families and individuals affected by ASD. In alignment with NIMH's strategic priorities, this mentored career development award aims to evaluate a clinically useful biobehavioral marker of ASD that can be translated to the development of new interventions to be delivered in infancy. The proposed research investigates the utility of a physiological measure of attention (?heart defined sustained attention?) as a neurobehavioral marker of later-emerging social-communication skills and ASD symptomology. The long-term goal of this research program is to develop an early biobehavioral marker of risk and a novel conceptual framework for early intervention, capitalizing on neuroplasticity that peaks in the infant months and diminishes significantly thereafter. Dr. Bradshaw has assembled an expert team of mentors that will guide her career development in order to (1) develop new expertise in theoretical foundations of developmental psychophysiology of attention in infants and ASD populations, (2) gain methodological proficiency in biobehavioral assessment- based technologies that will lead to a mechanistic understanding of the emergence of ASD, (3) acquire the knowledge and technical skills necessary for statistical analysis of complex longitudinal datasets that will reveal underlying typical and atypical developmental processes, and (4) build professional skills to launch a successful independent research career grounded in characterizing developmental trajectories and identifying clinically useful biobehavioral markers of ASD. Intensive, hands-on training in developmental psychophysiology, eye- tracking methodology, and longitudinal data analysis will enable the candidate to collect objective, specific, repeated measures of attention, beginning at a point in development when endogenous attention first emerges. In order to hone in on mechanistic pathways that link early social attention to later social communication, Aim 1 of the proposed study will use eye tracking and heart rate to characterize the emergence of sustained attention to social and non-social stimuli, and during social and non-social naturalistic interactions, in low-risk (LR) and high-risk (HR) infants at 3, 6, 9, and 12 months. Aim 2 will identify associations between early trajectories of heart defined sustained attention (from 3-12 months) and emerging social-communication skills and ASD features (from 9 to 24 months). The proposed research and career development aims will lead to novel conceptualizations of the pathogenesis ASD and, in line with the candidate's long-term career objectives, translate directly to the development of innovative intervention strategies for infants before their first birthday and the integration of assessment-based technologies into early intervention protocols.